The present invention relates to a process for producing a phenolic resin-made pulley having a metal insert embedded therein, as well as to a phenolic resin composition used in said process.
In automobiles, use of smaller and more lightweight parts is in progress in order to achieve improved fuel consumption, etc. Lighter weight and higher performance are required as well in mechanical parts such as piston, gear, pulley and the like; and switch from metal-made parts (e.g. parts made of die castings, sheet metals and sintered materials) to resin-made parts is under study.
As to the pulleys for automobiles, which are required to have belt abrasion resistance, dimensional precision and heat resistance, there have been studied, for example, polyamide resin-made or phenolic resin-made pulleys containing a glass fiber as the filler, and a phenolic resin-made pulley containing a cotton cloth as the filler (e.g. JP-A-64-87968).
These resin-made pulleys, however, have problems as follows. The polyamide resin-made pulley containing a glass fiber as the filler tends to cause melting and falling-off by the abnormal heat generated when slippage occurs between the pulley and a belt, and is therefore insufficient in reliability. The phenolic resin-made pulley containing a glass fiber as the filler has a detrimental drawback in that the pulley brings about belt abrasion easily.
The phenolic resin-made pulley containing a cotton cloth as the filler is superior in belt abrasion resistance, but has no sufficient strength when a solid or powdery resin is used and dry kneading is conducted because no sufficient impregnation of the filler with the resin is expected.
Under such a situation, it has been necessary to develop a phenolic resin-made pulley having excellent heat resistance, strength and abrasion resistance.
Resin-made pulleys are generally produced by compression molding or injection molding. In compression molding, the molded pulley has, in practical use, no problems in strength, etc.; however, the molding time is long and production of a plurality of pulleys is impossible, resulting in low productivity.
Meanwhile, in injection molding, productivity is high; however, pulley molding is generally conducted by utilizing pinpoint gates extending to the disc portion of a pulley to be molded. FIG. 3A shows a resin-made pulley molded by a pinpoint gate process. Such a pulley has a very small strength at the welded portions (22) about the metal insert (21) and accordingly does not fully satisfy the properties required when used as an important mechanical part of an automobile, etc. In the case of a pulley having holes (23) in the disc portion, as shown in FIG. 3B, the pinpoint gates (20) are inevitably provided near the metal insert-resin interfaces, allowing the pulley to have a further smaller strength.
In injection molding, use of a side gate process is considered. In this process, however, the welded portion is formed at the pulley portion opposite to the gate, and the strength at the welded portion is even smaller than that obtained in the pinpoint gate process. In the case of a pulley having holes, in particular, the pins used for forming the holes are provided as a part of the cavity so as to extend in the entire length of the cavity; therefore, in feeding a molding material into the cavity, the pins interrupt the smooth feeding of the molding material, a jumping phenomenon takes place at the pulley portion opposite to the gate, and the strength at the welded portion gets further smaller. In any rate, in injection-molding a phenolic resin-made pulley, the strength at the welded portion is inevitably small and such a pulley finds yet no practical application as a mechanical part of an automobile, etc.
As described above, the phenolic resin-made pulleys produced by injection-molding a conventional phenolic resin molding material are inferior in strength, etc. and do not satisfy the requirements therefor. The present invention is intended to provide a phenolic resin-made pulley free from the above-mentioned problems and having excellent productivity.
The present invention provides a process for producing a phenolic resin-made pulley having a metal insert embedded therein, which process comprises:
setting a metal insert in the form of a cylinder or a circular solid shaft in a cavity of a mold having a movable side die, a fixed side die and the cavity,
closing the mold in a state in which a part or the whole of the movable side die has been moved backward by a given distance from its predetermined position to be taken when a pulley to be produced has a final shape,
injecting a phenolic resin molding material into the cavity to fill the cavity with the molding material,
preferably sealing a gate of the mold with a gate-sealing pin, and substantially simultaneously with or after the gate sealing
moving forward the part or the whole of the movable side die moved backward, to said predetermined position to mold a phenolic resin-made pulley.
This process is particularly effective to mold a phenolic resin-made pulley having holes formed in its disc portion. Said pulley can be produced according to the above process, for example, by
closing the mold in a state in which pins used for forming said holes have been moved backward from their predetermined positions to be taken later,
injecting a phenolic resin molding material into the cavity to fill the cavity with the molding material,
preferably sealing a gate of the mold with a gate-sealing pin, and substantially simultaneously with or after the gate sealing
moving forward the pins to said predetermined positions to mold said pulley.